The disclosure of Japanese Patent Application No. 2001-331570 filed on Oct. 29, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates generally to a fluid-filled active vibration damping device having a pressure-receiving chamber filled with a non-compressible fluid and capable of actively offsetting or attenuating a vibrational load applied to the pressure-receiving chamber by suitably controlling a pressure of the fluid filling the pressure-receiving chamber. More particularly, the present invention is concerned with such a fluid-filled active vibration damping device that is suitably applicable to active elastic mounts or active dampers or oscillators for use in automotive vehicles.
2. Description of the Related Art
Vibration damping devices have been used for damping or isolating vibrations (including noises induced by the vibrations) of a subject member such as a body of an automotive vehicle or other members suffering from these vibrations or noises. Known examples of such vibration damping devices include: a vibration-damping coupling or mount, e.g., an engine mount, which is interposed between the subject member and a vibration source, e.g., a power unit, so as to connect these two members in a vibration damping or isolating fashion for eliminating or reducing a vibration transmitted from the vibration source to the subject member; and a vibration damper that is fixed to the subject member for attenuating or absorbing the vibration of the subject member.
A fluid-filled active vibration damping device has been proposed as one type of such vibration damping devices, which includes: an elastic body elastically deformed due to vibrational loads applied thereto; a pressure-receiving chamber partially defined by the elastic body and filled with a non-compressible fluid; an oscillating rubber plate disposed elastically displaceable; an oscillating fluid chamber partially defined by one of opposite sides of the oscillating rubber plate and filled with the non-compressible fluid; an orifice passage permitting a fluid communication between the pressure-receiving chamber and the oscillating fluid chamber; and a working air chamber partially defined by the other side of the oscillating rubber plate so as to be opposed to the oscillating fluid chamber with the oscillating rubber plate interposed therebetween. In the known fluid-filled active vibration damping device, an air pressure variation corresponding to vibrations to be damped is applied from the external area to the working air chamber so as to oscillate the oscillating rubber plate, and an oscillating force generated by the oscillation of the oscillating rubber plate is transmitted to the pressure-receiving chamber through the oscillating fluid chamber and the orifice passage, thus making it possible to actively control a fluid pressure variation induced in the pressure-receiving chamber. Thus, the known fluid-filled active vibration damping device is capable of exhibiting an active vibration damping effect or an offsetting effect with respect to vibrations to be damped, and accordingly ensuring high vibration damping characteristics in comparison with conventional passive vibration damping devices. For this reason, the known fluid-filled active vibration damping device has been applied to an engine mount for automotive vehicles where a demand for higher grade damping has been growing.
In order to induce in the working air chamber the air pressure variation having a frequency corresponding to that of the vibrations to be damped, the known fluid-filled active vibration damping device generally employs: an air conduit connectable to the working air chamber; and a solenoid-operated switch valve operable for alternately connecting and disconnecting the air conduit to and from two different air pressure sources, e.g., a vacuum source and the atmosphere, at a frequency corresponding to that of vibrations to be damped.
However, the conventional fluid-filled active vibration damping device is not able to conform the waveform of the air pressure variation induced in the working air chamber to the waveform of the vibrations to be damped with sufficient accuracy, since the air pressure variation is induced in the working air chamber as a result of the switching operation of the solenoid operated switch valve between the two different air pressure sources, namely the air pressure variation is caused by an xe2x80x9cON/OFFxe2x80x9d like operation of the solenoid operated switch valve. Also, undesirable pressure variation is likely to be generated due to compressibility of the air used as a pressure-transmitting medium. For the above reasons, the air pressure variation applied to the working air chamber is likely to include secondary frequency components other than a primary frequency component corresponding to the frequency of the vibrations to be damped, thereby undesirably transmitting to the pressure-receiving chamber the oscillating force having the secondary frequency components, which are not corresponding to the frequency of the vibrations to be damped. Therefore, the conventional fluid-filled active vibration damping device may possibly suffer from deterioration of its damping capability due to the generation of the secondary frequency components in the air pressure variation applied to the working air chamber.
It is therefore one object of this invention to provide a fluid-filled active vibration damping device, which is novel in construction and which is capable of reducing a transmission of a fluid pressure variation having higher frequency components or other frequency components that do not correspond to a vibration to be damped to a pressure-receiving chamber, for thereby exhibiting a desired active vibration damping effect in an effective and a stable manner.
The above and/or optional objects of this invention may be attained according to at least one of the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depending from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to these modes of the invention and combinations of the technical features, but may otherwise be recognized based on the teachings of the present invention disclosed in the entire specification and drawings or that may be recognized by those skilled in the art in the light of the present disclosure in its entirety.
The present inventors have conducted an extensive study and a multiplicity of experiments in an effort to solve the conventionally experienced problem or to explore a mechanism of generation of the fluid pressure variation having the higher frequency components in the pressure-receiving chamber. As a result, the present inventors discovered at first that the air pressure variation applied to the working air chamber is converted into the fluid pressure variation generated in the oscillating fluid chamber, and then is transmitted to the pressure-receiving chamber through the orifice passage while being influenced by shapes of the orifice passages in terms of pressure transmission characteristics including pressure transmission efficiency. Namely, the pressure transmission characteristics of the orifice passage may vary depending upon its shape. The present invention was developed as a result of a further extensive study on this finding.
(1) A fluid-filled active vibration damping device including: (a) an elastic body elastically deformed due to a vibrational load applied thereto; (b) a pressure-receiving chamber partially defined by the elastic body and filled with a non-compressible fluid; (c) an oscillating rubber plate disposed elastically displaceable; (d) an oscillating fluid chamber partially defined by the oscillating rubber plate, disposed on one of opposite sides of the oscillating rubber plate, and filled with the non-compressible fluid; (e) a first orifice passage for permitting a fluid communication between the pressure-receiving chamber and the oscillating fluid chamber; and (f) a working air chamber partially defined by the oscillating rubber plate and disposed on an other one of opposite sides of the oscillating rubber plate; wherein an air pressure variation having a frequency corresponding to that of a vibration to be damped is applied from an external area to the working air chamber so as to cause an oscillation of the oscillating rubber plate for actively controlling a pressure of the fluid in the pressure-receiving chamber via the oscillating fluid chamber and the first orifice passage, and wherein a ratio V/Q of a passage volume V of the first orifice passage to a unit flow amount Q of the fluid through the first orifice passage caused by the oscillation of the oscillating rubber plate based on the air pressure variation applied to the working air chamber is held within a range from 1 to 10.
In the field of fluid-filled active vibration damping devices to which the present invention is related, conventionally, a first orifice passage for permitting a fluid communication between a pressure-receiving chamber and an oscillating fluid chamber was suitably tuned depending upon a frequency of a vibration to be damped, in order to improve efficiency in transmitting a fluid pressure variation induced in the oscillating fluid chamber to the pressure-receiving chamber. More specifically, a known tuning of the orifice passage includes that a ratio A/L of a cross sectional area A of the orifice passage to a length L thereof is adjusted depending upon the frequency of the vibration to be damped. In the present mode of the invention, on the other hand, the shape of the first orifice passage is determined in view of the above-described unknown novel technical finding that the pressure transmission characteristics of the first orifice passage for the higher frequency components of the fluid pressure induced in the oscillating fluid chamber have a highly dependence on the shape of the first orifice passage. More specifically, the ratio V/Q of the passage volume V of the first orifice passage to the unit amount Q of flow of the fluid through the first orifice passage is held within a range of about 1-10. This arrangement permits the first orifice passage to exhibit an excellent filtering effect for preventing or minimizing undesirable transmission of the secondary frequency components of the frequency of the vibration to be damped from the oscillating fluid chamber to the pressure-receiving chamber. Accordingly, even if the air pressure variation applied to the working air chamber contains the higher frequency components which do not correspond to the frequency of the vibration to be damped, the first orifice passage can prevent or minimize the undesirable transmission of the higher frequency components to the pressure-receiving chamber. Thus, the engine mount of this mode of the invention can effectively exhibit a desired vibration damping or isolating effect with high stability while preventing deterioration of the vibration damping effect due to the undesirable transmission of the higher frequency components to the pressure-receiving chamber.
If the ratio V/Q is not larger than 1, it become difficult for the first orifice passage to sufficiently restrict the transmission of the secondary frequency components to the pressure-receiving chamber. If the ratio V/Q is not smaller than 10, the first orifice passage and the vibration damping device become large too much, so that it is improper for a practical use. It should be appreciated that the unit flow amount Q is interpreted to mean an amount of flow of the fluid through the first orifice passage when the oscillating rubber plate is displaced from the working air chamber side to the oscillating fluid chamber side.
(2) A fluid-filled active vibration damping device according to the above-indicated mode (1) of the invention, wherein the first orifice passage is tuned to a frequency range of the vibration to be damped, which is not less than 30 Hz. In a vibration damping device for use in an automotive vehicle, for example, the frequency range of not less than 30 Hz is recognized as a high frequency range corresponding to booming noises or the like. The orifice passage tuned to this high frequency range tends to have a relatively small length as a result of the above-described known tuning in an attempt to improve the transmission efficiency of the fluid pressure variation through the orifice passage. Therefore, the secondary higher frequency components of the fluid pressure variation induced in the oscillating fluid chamber as a result of the air pressure variation applied to the working air chamber are transmitted through the orifice passage to the pressure-receiving chamber at a high transmission rate, possibly resulting in considerable deterioration of the vibration damping capability of the vibration damping device. On the other hand, the fluid-filled active vibration damping device of this mode of the invention employs the first orifice passage specifically configured as defined in the above-indicated mode (1) of the invention. This first orifice passage permits a high transmission efficiency thereof for transmitting the fluid pressure variation from the oscillating fluid chamber to the pressure-receiving chamber with the help of resonance of the fluid flowing therethrough, while exhibiting the filtering effect with respect to the fluid pressure variation over the high frequency range, for thereby restricting or minimizing the transmission of the higher frequency components of the fluid pressure variation from the oscillating fluid chamber to the pressure-receiving chamber. Thus, the fluid-filled active vibration damping device of this mode of the invention can exhibit an active vibration damping or isolating effect with respect to vibrations over the higher frequency range of not lower than 30 Hz.
(3) A fluid-filled active vibration damping device according to the above-indicated mode (1) or (2), further comprising a partition member disposed on the one of opposite sides of the oscillating rubber plate with a spacing therebetween and separating the pressure-receiving chamber and the oscillating fluid chamber from each other, wherein the first orifice passage extends along a surface of the partition member. This mode of the invention makes it possible to provide a sufficient length of the first orifice passage by effectively utilizing a limited space, thereby assuring a high degree of freedom in designing the first orifice passage.
(4) A fluid-filled active vibration damping device according to any one of the above-indicated modes (1)-(3), further comprising an air pressure controller operable to alternately connect the working air chamber to a vacuum source and an atmosphere at a predetermined frequency corresponding to the frequency of the vibration to be damped, for alternately applying a negative pressure and an atmospheric pressure to the working air chamber. This mode of the invention makes it possible to employ the atmosphere as one of air pressure sources for use in application of the air pressure variation to the working air chamber, thus simplifying the structure of the fluid-filled active vibration damping device.
(5) A fluid-filled active vibration damping device according to any one of the above-indicated modes (1)-(4), wherein the device is adapted to be interposed between two members for elastically connecting the two members in a vibration damping fashion, and further comprises: a first mounting member attachable to one of the two members; a second mounting member attachable to an other one of the two members and opposed to the first mounting member with a spacing therebetween, the first and second mounting members being elastically connected with each other by the elastic body interposed therebetween; an equilibrium chamber partially defined by a flexible layer and filled with the non-compressible fluid; and a second orifice passage for permitting a fluid communication between the equilibrium chamber and the pressure-receiving chamber. This mode of the invention is able to effectively provide fluid-filled active vibration damping couplings (bushings) or mounts used for automotive vehicles, such as an engine mount, a body mount, a member mount and a suspension bushing. In particular, the fluid-filled active vibration damping device includes the equilibrium chamber whose volume is easily variable. This makes it possible to absorb or reduce an increase in the fluid pressure in the pressure-receiving chamber and the oscillating fluid chamber due to the elastic deformation of the elastic body owing to a pressure absorbing effect of the equilibrium chamber when a static load is applied to the device, e.g., when a weight of a power unit is applied to an engine mount for an automotive vehicle. Thus, the fluid-filled active vibration damping device of this mode of the invention can exhibit an intended vibration damping or isolating effect with high stability.
(6) A fluid-filled active vibration damping device according to any one of the above-indicated mode (5), further comprising: a third orifice passage for permitting a fluid communication between the pressure-receiving chamber and the equilibrium chamber, that is disposed in a parallel relationship with the second orifice passage, and that is tuned to a frequency range higher than that of the second orifice passage; and a shut-off valve operable for permitting and inhibiting a fluid communication through the third orifice passage while permitting a fluid communication through the second orifice passage. According to this mode of the invention, the fluid-filled active vibration damping device is able to exhibit a vibration damping or isolating effect based on flow of the fluid through the second orifice passage, with the third orifice passage closed by means of the shut-off valve. Also, the fluid-filled active vibration damping device is able to exhibit a vibration damping or isolating effect with respect to vibrations over the frequency range higher than the frequency range to which the second orifice passage is tuned, based on flows of the fluid through the third orifice passage, with the third orifice passage open by means of the shut-off valve. That is, the fluid-filled active vibration damping device of this mode of the invention is capable of alternatively exhibiting passive vibration damping and/or isolating effects based on flows of the fluid through the second orifice passage and the third orifice passage, by alternatively inhibiting and permitting the fluid communication through the third orifice passage. In addition, the oscillating rubber plate is suitably oscillated so that the fluid-filled active vibration damping device can exhibit a desired active vibration damping or isolating effect, effectively. By effectively utilizing these passive and active vibration damping or isolating effects, the fluid-filled active-vibration damping device is able to selectively exhibit the vibration damping and/or isolating effects with respect to vibrations over three different frequency ranges, with a simple structure. Alternatively, the fluid-filled active-vibration damping device is able to simultaneously exhibit vibration damping or isolating effect with respect to vibrations over a plurality of different frequency ranges.
In the fluid-filled active vibration damping device according to the mode (6) of the invention, the oscillating rubber plate may be oscillated at a frequency corresponding to a high frequency range of the vibration to be damped to which the first orifice passage is tuned, by applying a desirable air pressure variation applied to the working air chamber. Also, the oscillating rubber plate may be oscillated at the frequency to which the second or the third orifice passage is tuned, by applying a desirable air pressure variation applied to the working air chamber, for thereby improving the passive vibration damping or isolating effects with respect to vibrations over the frequency ranges to which the second and third orifice passages are tuned.
(7) A fluid-filled active vibration damping device according to the above-indicated mode (6), wherein an opening of the third orifice passage to the equilibrium chamber is located at a position different from a position of an opening of the second orifice passage to the equilibrium chamber, and the shut-off valve comprises a pneumatically operated actuator disposed so as to be opposed to the opening of the third orifice passage with the flexible layer interposed therebetween, the pneumatically operated actuator being operable to move the flexible layer toward and away from the opening of the third orifice passage for closing and opening the opening of the third orifice passage, in order to permit and inhibit the fluid communication through the third orifice passage. According to this mode of the invention, a driving device of the shut-off valve can be provided by the pneumatically operated actuator, which is simple in construction and light in weight. The use of the actuator further simplifies the structure of the fluid-filled active vibration damping device of this mode of the invention.
(8) A fluid-filled active vibration damping device according to the above-indicated mode (6) or (7), wherein the device is applied to an engine mount for use in automotive vehicles, and the first orifice passage is tuned to a frequency range corresponding to booming noises, the second orifice passage is tuned to a frequency range corresponding to engine shakes, and the third orifice passage is tuned to a frequency range corresponding to engine idling vibrations. According to this mode of the invention, the engine mount is capable of exhibiting passive vibration isolating and damping effects based on resonance or flows of the fluid through the third and second orifice passages with respect to the engine idling vibrations and the engine shakes, which are likely to be excited in an idling condition and a running condition of the vehicle, respectively. With respect to the booming noises or other high frequency vibrations, which are likely to be excited in the running condition of the vehicle, the engine mount can also exhibit an active vibration isolating effect by actively controlling the fluid pressure in the pressure-receiving chamber based on the air pressure variation applied to the working air chamber. In particular, the transmission of the higher frequency components of the air pressure variation applied to the working air chamber can effectively eliminated or reduced owing to the filtering effect of the first orifice passage, thus eliminating the problem of deterioration of the vibration damping capability of the engine mount due to the undesirable transmission of the high frequency components to the pressure-receiving chamber. Thus, the fluid-filled active vibration damping device is capable of exhibiting an excellent vibration damping or isolating effect with respect to vibrations over a wide frequency range with high stability.